This invention relates to a process for separating aluminum from an aluminum containing two-phase mixture. More particularly, this invention concerns itself with an electrolytic process for removing aluminum from a two-phase matrix consisting of aluminum and trialuminum nickelide.
The inclusion of a controlled eutectic alloy of trialuminum nitride within an aluminum body has been found to be an effective means of providing tensile strength enhancement for the aluminum. The alloy is grown within the aluminum body as an aligned microstructure in the form of whiskers. In addition to providing improved tensile strength, the whiskers of Al.sub.3 Ni also find useful application in industrial and military microelectronics if they can be removed undamaged from the aluminum matrix in which they are embedded.
A number of methods are utilized for producing Al.sub.3 N.sub.i whiskers in an aluminum matrix. One utilizes a unidirectional solidification technique; whereas, another grows Al.sub.3 Ni fiber bundles longitudinally in a rod-shaped aluminum matrix. Still other methods are contemplated and a considered research effort is being conducted in an attempt to develop even more efficient means of growing these useful fibers. A fundamental problem exists, however, in the removal and separation of the fibers from the Al-Al.sub.3 Ni two phase matrix within which they are formed. Therefore, a need exists for the development of an efficient and practical removal method in order to study the effectiveness of prior art procedures as well as those concerned in the future. Also, the usefullness of these fibers for microelectronic application is severely limited unless a means can be developed for their removal from the matrix without damage.
In previous methods, aqueous electrolyte or acid etches were utilized for removing or dissolving aluminum from an Al-Al.sub.3 Ni matrix. Unfortunately, these methods have always been accompanied by gas evolution resulting in "birdsnesting" of the fiber bundles as they are exposed. Still another problem encountered in using aqueous acid etches is their low selectivity of attack. For example, the Al.sub.3 Ni fibers are dissolved as well as the bulk aluminum. It becomes obvious, therefore, that an electrolyte that could sustain aluminum electrolysis without gas evolution while permitting selective attack on the bulk aluminum phase would circumvent the problems encountered in using prior art methods of separation.
After a considerable research effort, the problem of providing an efficient and effective means of separating aluminum from a two-phase matrix of aluminum and trialuminum nitride filaments has been solved by the electrolytic process of this invention. A molten salt electrolyte which contains an aluminum halide is used as the electrolyte and removal is effected by passing a current between an inert cathode and an anode composed of the two-phase Al-Al.sub.3 N matrix.